GATE AG 2025 • Q32 NAT • 1 Mark

Section 6: Agricultural Process Engineering

Evaporation and Drying

Subtopic: Drying kinetics

Question Statement:

Apple slices dry from 65% (d.b.) to 10% (d.b.) in a hybrid solar dryer, falling rate period, drying rate constant = 1/104 min⁻¹, equilibrium moisture content 2% (d.b.). Find the drying time (min). (Rounded to 2 decimal places)

Official Answer Key:

214 to 215

Step-by-Step Solution & Explanation

In the falling-rate period, moisture ratio decays exponentially: (M−Me) = (M0−Me)e^(−kt). t = (1/k)·ln[(M0−Me)/(M−Me)] = 104×ln[(65−2)/(10−2)] = 104×ln(7.875) = 104×2.0637 = 214.62 min.

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